1. Field of the Invention
The present invention relates to fuel injection for direct injection spark ignition internal combustion engines.
2. Background Art
Direct-injection spark-ignition (DISI) internal combustion engines have been developed to reduce fuel consumption and feedgas emissions of gasoline engines. DISI combustion technologies can generally be classified as either homogeneous charge or stratified charge systems. In homogeneous charge systems, the engine operates only in the homogeneous mode where the air-fuel mixture of the charge in the combustion chamber is generally well-mixed or homogeneous throughout the chamber. Stratified charge combustion systems operate in a stratified mode with layers or strata of richer air/fuel ratio near the spark plug and progressively leaner layers below under certain operating conditions, such as low to medium load and low to medium engine speed, for example, while operating in a homogeneous mode otherwise. Systems designed for homogeneous mode operation generally use an injector having an evenly distributed fuel spray that is well mixed with air to create a homogeneous charge. Systems designed for stratified charge mode operation require the richer fuel-air mixture in the region of the spark plug gap location and generally use an injector having jets closely arranged to form a suitable fuel cloud around the spark plug. To operate in the homogeneous mode, stratified charge systems may require design compromises or additional devices such as a variable charge motion control device or air assisted injection to achieve sufficient charge homogeneity. These design compromises generally increase complexity and associated cost and may lower the efficiency of stratified mode operation.